1. Field of the Invention
This invention relates to leakage free bushings, and more particularly to vacuum tight valves and rotating bushings for use as fittings.
2. Description of the Prior Art
In devices which operate in accordance with vacuum technology, leakage free valves and rotating bushings have been employed for a relatively long period of time. Traditionally, such valves consist of moveable metal bellows which, in the axial direction, are stretched or elongated by a screw or tilt device so that a moveable sealing element can be separated from or pressed against a stationary sealing seat. Valves that are constructed in accordance with this principle have been customarily used as fittings when high pressure and vacuum pressure is a consideration.
A significant drawback of the traditional vacuum bushings is that they are relatively difficult to manufacture and as a result, they are significantly more expensive as compared to non-vacuum sealed fittings. A further disadvantage of the traditional vacuum bushing resides in that the medium which flows through the valve is severely deflected as it travels through the valve body. As a result, significant turbulence is generated which further increases the flow resistance and decreases the flow rate of the medium through the valve.
Furthermore, it is known to configure vacuum tight bushings having an angular movement of the bellows. Such devices are even more difficult to manufacture than the above-mentioned fittings since the angular movement must be supported by at least one fulcrum.